Vascular stent devices and methods

ABSTRACT

Described here are devices, systems, and methods for cannulating a vessel. Generally, the method may comprise advancing a stent into a first vessel and deploying the stent in the first vessel to hold open one or more valves. This may permit retrograde blood flow through the blood vessel in peripheral vasculature and aid in cannulation of the blood vessel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/399,465, filed on Sep. 25, 2016, and titled “VASCULAR STENTDEVICES AND METHODS,” the content of which is incorporated by referencein its entirety.

FIELD

The current invention relates to stents and methods for cannulating avessel.

BACKGROUND

An intravenous cannula provides access to a vein and may allow blood tobe drawn and fluids to be administered into a patient. In the case ofhemodialysis, cannulation provides access to a fistula with quickenedblood flow that may provide for effective dialysis. In dialysistreatment, needles, catheters, or other cannulas may be inserted intothe blood vessels near a fistula to draw blood from the circulatorysystem, pass it through a dialysis machine, and return it to the body.However, cannulation can be difficult due to challenges in locatingvessel sites, difficulty reaching vessels for vascular access due to anunderlying layer of adipose tissue, collapse of a blood vessel beingpunctured, and complications from cannulation that may include hematoma,infiltration, thrombosis, and embolism. It would therefore be useful tofind improved ways to access the vasculature for cannulation, and waysto modify blood flow to allow for alternative access sites, such as toimprove access to blood vessels near a fistula.

BRIEF SUMMARY

Described here are devices, systems, and methods for improvingretrograde blood flow through peripheral vasculature and to aid incannulation. The devices, systems, and methods described herein may beused to hold open venous valves to allow bi-directional flow of bloodthrough a vein. In some variations, a stent may be deployed in a bloodvessel to hold open a valve to increase retrograde blood flow, aid inlocating the blood vessel, and structurally support the blood vesselduring cannulation. In some variations, a fistula may be formed toarterialize a vein and increase retrograde blood flow through the vein.In some variations, the methods described herein comprise methods forcannulating a first vessel comprising advancing a stent into the firstvessel comprising one or more valves. The stent may be deployed over oneor more valves to hold open the one or more valves. A needle may beadvanced through a wall of the first vessel. In some variations, theneedle may also be advanced through an aperture defined in a wall of thestent. In other variations, the needle may be advanced through the wallof the first vessel at a location distal to the stent. In somevariations, stent location may be detected non-invasively. In some ofthese variations, the needle may be positioned over the first vesselusing the detected stent location. In other variations, the stentcomprises first struts and second struts having different thicknesses.In some variations, the first vessel may be a cephalic vein. In othervariations, the first vessel may be a basilic vein.

In some variations, a first catheter may be advanced into an arteryadjacent to a vein. The first catheter may comprise a fistula-formingelement, and a fistula may be formed between the artery and the veinusing the fistula-forming element. The stent may be deployed distal tothe fistula. The artery may be an ulnar artery and the vein may be anulnar vein. A second catheter may be advanced into the vein. In someinstances, the first catheter and the second catheter may be aligned.One or more stents may be loaded into a third catheter. The one or morestents may be sequentially deployed from the third catheter into thefirst vessel by advancing a push wire through the third catheter.

Also described here are systems for forming a fistula and improvingretrograde blood flow through peripheral vasculature. In general, thesystems described herein may include a catheter system comprising astent comprising one or more apertures defined in a wall of the stent.The stent may be configured to hold open one or more venous valves andreceive a needle through one or more apertures. A first catheter maycomprise a fistula-forming element. In some variations, the stent maycomprise first struts and second struts having different thicknesses.The system may further comprise a plurality of the stents and a secondcatheter comprising a push wire configured to deploy one or more stentssequentially from a distal end of the second catheter. Thefistula-forming element may be an electrode. The needle may be acannula. The system may further comprise a stent detector coupled to aneedle injector coupled to the needle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative depiction of the vascular anatomy of the arm.

FIGS. 2A-2F depict illustrative variations of a stent.

FIG. 3 depicts an illustrative variation of a system described herecomprising a stent detector and cannulator.

FIG. 4 depicts an illustrative variation of a system described herecomprising a first catheter and a second catheter.

FIGS. 5A-5D depict an illustrative variation of a method for cannulatinga vessel.

FIG. 6 depicts an illustrative variation of a stent delivery system.

FIGS. 7A-7E depict illustrative variations of a method for delivering astent.

DETAILED DESCRIPTION

Generally described here are devices, systems, and methods for providinga stent in peripheral vasculature to permit retrograde blood flow, tosupport cannulation of a vein, and/or to percutaneously create one ormore arteriovenous fistulae for increasing venous blood flow, such asfor increasing retrograde blood flow through a forearm vein to becannulated. Accordingly, it may be helpful to briefly describe theanatomy of the vasculature of the arm.

FIG. 1 shows a simplified depiction of the typical vascular anatomy ofthe arm around the elbow. Specifically, FIG. 1 shows an anterior view ofthe right arm as would be seen with the palm facing upward. As shownthere, the brachial artery (100) extends superficially and distally fromthe upper arm and sinks deeply into the arm near the elbow joint, wherethe brachial artery (100) branches into the radial artery (102) and theulnar artery (104). The upper portion of the ulnar artery (104) isdeeply seated within the arm beneath the superficial flexor muscles (notshown), and leads down the ulnar side of the forearm to the wrist. Theanterior ulnar recurrent artery (106) and the posterior ulnar recurrentartery (108) branch off of the ulnar artery (104) just below the elbowjoint, and these arteries supply blood to the joint and surroundingmuscles. Further down the arm (typically just below the radialtuberosity of the radius bone (not shown)), the interosseous artery(109) branches off from the ulnar artery (104) and eventually feeds intothe posterior and anterior interosseous arteries.

Also shown in FIG. 1 are the cephalic vein and the basilic vein. Thecephalic vein runs along the outer border of the bicep muscle (notshown) continues down into the forearm (the cephalic vein of the upperarm is labeled in FIG. 1 as cephalic vein (110), while the cephalic veinof the lower arm is labeled as cephalic vein (114)). The median cephalicvein (116) joins the cephalic vein2 (110, 114) near the elbow joint. Thebasilic vein runs along the inner side of the bicep muscle and continuesinto the forearm (the basilic vein of the upper arm is labeled asbasilic vein (112), while the basilic vein of the lower arm is labeledas common ulnar vein (120)). The basilic vein (120) of the lower arm issometimes referred to as the common ulnar vein. The median cubital vein(118) (in some instances referred to as the median basilic vein) joinsthe basilic vein (112) and the common ulnar vein (120) (in someinstances, this vein segment is also referred to as the basilic vein ofthe forearm). The median cubital vein (118) and the median cephalic vein(116) are formed at the branching of the median antebrachial vein (122).Near the branching of the median vein (122) into the median cubital vein(118) and the medial cephalic vein (116), a perforating branch (124)connects these vessels with the deep veins of the arm through theantebrachial fascia (not shown). As shown in FIG. 1, perforating branch(124) communicates with a first deep ulnar vein (126) and a second deepulnar vein (128). These deep ulnar veins (126, 128) may runsubstantially parallel on either side of the ulnar artery (104) betweenthe brachial artery (100) and the interosseous artery (109), and maybranch away from ulnar artery (104) distal to the interosseous artery(109). Between the brachial artery (100) and the interosseous artery(109), the deep ulnar veins are typically located in close proximity tothe ulnar artery, and usually less than 2 mm separate the ulnar arteryfrom the deep ulnar veins. Along the length of the deep ulnar veins,transverse branches (not shown) may occasionally connect the deep ulnarveins. Also shown in FIG. 1 are first brachial vein (130) and second(132) brachial vein. The brachial veins generally run along the brachialartery (100), and the deep ulnar veins feed into the brachial veins nearthe elbow joint. Additionally, a pair of radial veins (not shown) mayrun along the radial artery, and may feed into one or both of thebrachial veins.

Generally, the systems, devices, and methods described herein may beused to hold open venous valves to permit retrograde blood flow in ablood vessel, to assist in locating a vascular access site, and/or toprovide structural support to a blood vessel to aid in cannulation(e.g., needle puncture into the blood vessel). In some variations, oneor more of these uses may be in conjunction with formation of a fistulabetween two blood vessels (e.g., an arteriovenous fistula between anartery and a vein). In some variations, a delivery system may beutilized to deploy one or more structures (e.g., stents) in a targetblood vessel where the deployed structures may increase blood flow andaid in cannulation.

Generally, the systems and methods may be used to hold openunidirectional venous valves in a vein to allow arterialized blood flow(e.g., from an arteriovenous fistula between an artery and a vein) totravel distally through the vein and provide a preferred conduit forretrograde blood flow. Generally, to create a retrograde blood flow paththrough a vein, a stent may be advanced in a minimally invasive mannerthrough the vasculature to a peripheral vein (e.g., a vein segment inthe forearm). The stent may be placed in the peripheral vein to holdopen one or more venous valves to permit retrograde blood flow. Forexample, the sidewalls of the stent may push one or more unidirectionalvalves against the inner circumference of the vein so as to hold openthe valves in the vein without damaging them. Opening the valves using astent may allow blood to flow retrograde through the vein withoutremoving the venous valves, as would be required in a valvulotomyprocedure. For example, opening the valves using a stent may allowarterialized blood flow from a fistula to flow retrograde through thevein without removing the venous valves. As the venous valves in therest of the peripheral vasculature retain their function and inhibitretrograde flow, the portion of the vein having the stent provides apreferred retrograde blood flow pathway. The devices and systemsdescribed herein offer a reversible approach to rendering valvesincompetent having improved procedural speed relative to a valvulotomethat cuts the leaflets of the valves. In some instances, a single stentmay be placed in a blood vessel. In other instances, a system comprisingmultiple stents may be deployed in one or more blood vessels. Forexample, in some instances, a stent may be placed in each of two veins(e.g., a cephalic vein and a basilic vein). In other instances, a stentmay be placed in a vein and an accessory vein. It should be appreciatedthat each stent may or may not have the same configuration of elements,and that some stents may be different from and/or complementary to otherstents.

Also generally described are systems comprising one or more stents toaid in cannulating a blood vessel by reducing damage and/or preventingcollapse of the blood vessel being punctured. The stent may add radialstrength and stiffness to the blood vessel in which it is disposed.These stents may be the same or different stents as those allowingretrograde venous blood flow. The one or more stents generally comprisea plurality of struts and may vary in length, diameter, thickness,geometric patterns, compressibility, and flexibility based on a targetvessel, function, and delivery process. The stent may comprise acannulation region having one or more apertures defined in a wall of thestent configured to receive a needle such as for cannulation.

Generally, the devices, systems and methods described herein may be usedto cannulate a vein, such as a forearm vein. Generally, a stent may beadvanced in a minimally invasive manner through the vasculature andplaced in the vein. The stent may add to the strength and stiffness ofthe vein segment in which the stent is disposed, such as when beingpunctured by a needle. In some instances, the vein may be palpatedand/or visualized to locate one or more of the stent and vein forcannulation. In other instances, the system may comprise a stentdetector to non-invasively detect the stent disposed in the vein. Forexample, the stent detector may generate a signal when the presence ofthe stent is detected through the skin of the patient and output thesignal to an operator. In some of these instances, a stent may define acannulation region through which a needle may be advanced. Once a veinis located, an insertion point may be selected for a cannula such as aneedle. The needle may be advanced through the skin and a vessel wall ofthe vein and an aperture defined in a wall (e.g., sidewall) of thestent. By advancing the needle through the vessel wall and stent havingenhanced strength and stiffness, complications from cannulation such asinfiltration, hematoma, and vein wall collapse may be reduced.

Generally, the systems described herein may comprise a stent detectorand cannulator. These devices and systems may detect and locate theblood vessel for cannulation in cases where visualization and palpationare insufficient. In some variations, the stent detector may comprise ametal detector configured to detect a metal stent disposed in a vein. Insome variations, the stent detector may comprise an output device toindicate to an operator the detected location of the stent under theskin. The cannulator (e.g., needle injector) may be coupled to a needlethat may be advanced through skin and into a wall of a blood vessel andan aperture defined in a wall of the stent. In some instances, thesystem may output an audio tone when the system is located over thestent in the blood vessel.

Generally, one or more stents may be advanced in a minimally invasivemanner through the vasculature and placed in the vein using a stentdelivery system. These devices and systems offer a minimally invasiveapproach that may improve procedural speed by permitting deployment ofone or more stents using a single catheter and deployment to smallerdiameter blood vessels. Generally, to deliver and deploy one or morestents, one or more catheters may be advanced in a minimally invasivefashion through the vasculature to a target location. In some instances,a single catheter may be advanced to a target site in a blood vessel todeploy one or more stents. In other instances, a system comprisingmultiple catheters may be used to deliver and deploy one or more stentsto target sites in respective blood vessels. For example, in someinstances a catheter may be placed in each of the two blood vessels(e.g., different veins). One or both of the catheters may comprise apush wire (e.g., guidewire, stylet, push rod). The push wire may beconfigured to slide within the catheter to advance one or more stentsout of a lumen of the catheter for deployment of a stent. For example,one or more stents may be loaded into a lumen of the catheter distal tothe push wire. The stent may be configured to self-deploy to apredetermined shape when advanced out of the catheter and into a targetblood vessel by the push wire. For example, a distal tip of the pushwire may push a proximal end of the stent through a catheter lumen andout the distal end of the catheter. In these instances, it should beappreciated that each catheter may or may not have the sameconfiguration of elements, and that some catheters may be different fromand/or complementary to other catheters.

Generally, the systems and methods may be used to form and access afistula in peripheral vasculature, such as in a forearm. These devicesand systems offer a minimally invasive approach that may improveprocedural speed. Generally, to form one or more fistulas between twoblood vessels, one or more catheters may be advanced in a minimallyinvasive fashion through the vasculature to a target location. In someinstances, a single catheter may be placed in a blood vessel to form afistula with an adjoining blood vessel. In other instances, a systemcomprising multiple catheters may be used to form one or more fistulas.For example, in some instances a catheter may be placed in each of thetwo blood vessels (e.g., an artery and a vein). One or both of thecatheters may comprise a fistula-forming element. The fistula-formingelement(s) may comprise an electrode that is used to form the fistulasuch as through tissue ablation. The catheter may further comprise oneor more alignment portions including magnets that help align onecatheter relative to another catheter in related blood vessels and/orbring the catheters (and blood vessels) in closer approximation. Inthese instances, it should be appreciated that each catheter may or maynot have the same configuration of elements, and that some catheters maybe different from and/or complementary to other catheters.

I. Systems

The systems described here may comprise one or more stents to hold openone or more valves of a venous blood vessel, provide structural supportto a vein in which it is disposed, and/or aid in access for cannulation.Generally, the stents may comprise a plurality of struts forming acylindrical configuration. The stent may be placed in a blood vessel tohold the valves in an open configuration that allows bi-directionalblood flow, and in particular, retrograde blood flow through a vein.Accordingly, it may be desirable that the stent have sufficient radialstrength to hold open the valves, but be of minimal thickness andsurface area (e.g., diaphanous) to limit platelet activation andstenosis. The radial strength, thickness, and surface area of the stentsdescribed herein may be significantly less than that of vascular stentsfor maintaining the patency of blood vessels. In some variations, astent may hold one or more valves open, allow at least one of blood flowfrom a fistula and a needle to pass through an aperture defined in asidewall of the stent, and provide structural support to the fistula.

A. Stent

FIGS. 2A-2F show illustrative variations of stent geometries that may beused to increase retrograde blood flow in venous vasculature. FIG. 2Ashows a portion of a stent (200). As shown there, the stent (200) maycomprise a plurality of struts (204) forming a repeating symmetricdiamond pattern, which forms a cylindrical configuration (202). Itshould be understood that many different configurations of the stentpattern may be used to provide a structure capable of holding the valveleaflets open. Patterns may include a helical coil or coils, rings ofstraight, angled, zig-zag, or curved geometries interconnected bylinking elements, or braided or woven meshes.

Another variation is illustrated in FIG. 2B, which shows a portion of astent (210) comprising a plurality of first struts (214) and a pluralityof second struts (216) forming a cylindrical configuration (212). Thefirst struts (214) may be thicker (e.g., have a larger diameter) thanthe second struts (216). In one example, the first struts (214) may forma first set of diamonds and the second struts (216) may form a secondset of diamonds within the larger diamonds. As shown, nine smallerdiamonds form a larger diamond. In some variations, the second struts(216) may be disposed on the interior side of the first struts (214).The first struts (214) may be configured to provide radial strength to ablood vessel in which the stent (210) is disposed. The second struts(216) may be configured to hold open the valves. In some variations, oneor more of the larger diamonds formed by the first struts (214) may beformed without second struts (216) such that the larger diamond definesan aperture (not shown). The first and second struts (214, 216) thusform the sidewalls of the stent. An example of struts defining anaperture is further described herein. In yet another variation, as shownin FIG. 2C, a stent (220) may comprise a helical configuration. Forexample, the stent (220) may comprise a double helix (222) comprisingtwo or a plurality of helical elongate struts (224) and a plurality ofconnecting struts (226).

FIGS. 2D-2F illustrates a portion of a stent (230) comprising aplurality of struts (232) arranged to form one or more apertures (234)defined in a wall of the strut and disposed along a length of the strutand configured to receive a needle (240). For example, the struts (232)may form a quadrilateral aperture (234). In some variations, theaperture (234) may be configured to receive a needle (240) having adiameter between about 12 gauge and about 20 gauge. In some variations,the struts (232) forming the aperture may add radial stiffness tolocally support a wall of the vein being punctured by the needle (240)to allow the vein to be punctured without collapsing. A needle advancedthrough a wall of a target blood vessel may be further advanced throughan aperture (234) of the stent (230) without contact and/or damage to astrut (232). As such, the stent (230) may form a cannulation regionalong its length through which a needle (240) may preferably beadvanced.

In some variations, the stents may be configured with dimensions to holdopen venous valves and/or support the vessel during cannulation. In somevariations, the stent may have an outer diameter between about 1 mm andabout 20 mm. For example, the stent may have an outer diameter of about5.0 mm. In some variations, the stent may have a strut width andthickness between about 0.05 mm and about 0.5 mm. In some variations,the stent may have side aperture openings disposed in a plane parallelto a longitudinal axis of the strut (e.g., the apertures beingsubstantially orthogonal to the longitudinal axis of the strut) having alength between about 1 mm and about 15 mm and a width between about 1 mmand about 15 mm. For example, the stent may have an outer diameter ofabout 5.0 mm, a strut width of about 0.05 mm, a strut thickness of about0.05 mm, and one or more diamond shaped apertures about 5 mm in widthand about 10 mm in length.

In some variations, an axial portion of the stent may comprise aplurality of struts. For example, an axial portion of the stent maycomprise a minimum of four struts to provide a predetermined minimumstrut-to-leaflet ratio to achieve adequate valve leaflet opening whendeployed in a vein. In some instances, the strut width and mesh densityof the stent may be minimized so as to achieve a minimum stentarea-to-intimal area ratio. In some variations, the strut surfacearea-to-vessel wall surface area ratio may be between about 0.02 andabout 0.08. In some instances, this ratio may be between about 0.03 and0.04. The stent may comprise any suitable configuration, such as acylindrical configuration (e.g., tube) and/or helical spiralconfiguration. In some variations, the stent may have a length betweenabout 5.0 cm and about 60 cm. For example, the stent may have a lengthof about 15.0 cm. The stent may be configured to fit within a lumen of atarget blood vessel and press against the leaflets of a valve, such thatthey are moved into and held in an open configuration until the stent isremoved.

The stent may be made of any suitable material, for example, one or moremetals or polymers (e.g., stainless steel 316L, tantalum, nitinol,platinum iridium, niobium alloy, cobalt alloy, etc.). The stent mayoptionally be bioresorbable (e.g., made of poly-L lactic acid (PLLA) andmay absorb over a time period of six months to three years) and mayoptionally comprise a drug eluting coating configured to preventstenosis and/or thrombosis). The stent may be formed by any suitablemanufacturing process, for example, laser cutting, photochemicaletching, braiding, knitting, vapor deposition, water jet, etc. In somevariations, the stent may comprise one or more coverings and/orvisualization markers to aid in locating and positioning the stentwithin a vessel. For example, the stent may comprise a radiopaque markerand/or coating made of one or more of gold, platinum, tantalum, etc.that may be indirectly visualized.

In some variations, the stent may comprise multiple portions, eachportion corresponding to a specific material, shape, and/or coating. Forexample, the stent may comprise a proximal portion comprising a coatingfor inducing thrombosis, a distal portion configured to prevent plateletaggregation and maximize fluid flow through the vessel, and anintermediate portion comprising a radiopaque marker surrounding anaperture and configured to permit visualization to aid in locating ablood vessel for cannulation. Of course, the stent may comprise anysuitable number of portions (e.g., two, three, or four portions) and thelength of each portion may be the same or different from the otherportions. The stent may comprise any suitable length, and the length ofthe stent may vary depending on the type of procedure being performed.

In some variations, one or more portions of the stent may comprise avisual detection portion for indirectly visualizing the location and/ororientation of a stent with respect to a catheter system, target bloodvessel, and/or external elements such as a cannulator. The visualdetection portion may be visualized using a technique such asfluoroscopy during stent deployment and/or needle puncture of the bloodvessel. In some instances, one or more characteristics of the stent suchas echogenicity, radiopacity, surface area, surface area, permittivity,conductivity, permeability, and the like may be selected to enhancedetection by, for example, fluoroscopy and/or a stent detector describedherein. Fluoroscopy is a technique for real-time X-ray imaging where,generally, an X-ray beam is emitted from a fluoroscope through an areaof interest in a body. Objects to be visualized (e.g., stents) may beimaged using an image intensifier. A user viewing the real-time imagesshown by the image intensifier may then determine the location andorientation of the one or more stents and use it to guide stentdeployment and/or needle insertion.

Generally, a visual detection portion may be configured such that anaperture defined in a wall of the stent is discernable in atwo-dimensional fluoroscopic image and/or detectable by a stentdetector. In some variations, the portions of the stent configured fornon-invasive detection may be used to guide positioning of a needle tobe inserted through an aperture of the stent and the vessel wall. Forexample, one or more detection portions of the stent may surround anaperture of the stent and/or be provided at a predetermined locationcorresponding to the aperture. In some instances, the detection portionsof the stent may comprise a set of patterns that may be visualized underfluoroscopy. For example, the visual detection portion may comprise anellipsoid or polygon that may be fluoroscopically imaged. The shape ofthe visual detection portion may vary on a fluoroscopic image based onan orientation of the stent relative to the image intensifier. Forexample, a circular visual detection portion surrounding an aperture ofthe stent that appears as an ellipsoid on a fluoroscopic image mayindicate that the aperture is non-perpendicular with respect to theimage intensifier. Accordingly, the visual detection portion may be usedto guide placement of a stent in a target blood vessel and/or cannulainsertion through an aperture of the stent.

B. Stent Detector

The systems described here may comprise one or more of a stent detectorconfigured to locate a stent disposed in a vessel and a cannulator(e.g., needle injector) configured to advance a needle through a wall ofthe blood vessel and the stent. FIG. 3 illustrates a side view of acannulation system (300). As shown in FIG. 3, a stent detector (300) maycomprise a sensor (310) configured to detect a stent, an output device(320) configured to output a stent detection status, a cannulator (330),and a needle (340). The sensor (310) may be configured to non-invasivelydetect a location of a stent disposed in a blood vessel to aid anoperator in positioning the cannulator (330) and the needle (340) forcannulation. In some variations, the sensor (310) may comprise a metaldetector configured to generate a stent signal in response to detectinga metal content of a stent disposed in a blood vessel. In someinstances, the sensor (310) may comprise an inductive sensor. In somevariations, the stent detector (300) may comprise an optical sourceconfigured to project a light into the skin and an optical sensorconfigured to receive the reflected light from the skin that is used togenerate the stent signal.

The output device (320) may receive the stent signal and use it togenerate a signal to indicate that the stent has been located within apredetermined volume of space (e.g., the stent is directly beneath thelocation of the stent detector (300)). The output device (320) mayoutput one or more signals to indicate a location of the stent relativeto the stent detector (300). For example, the output device (320) maygenerate one or more audible tones and/or beeps to indicate proximity toa stent. In some variations, a set of colored lights may be output bythe output device (320) to visually indicate a distance between thestent detector (300) and the stent. In some instances, the color,pattern, intensity, and number of lights may correspond to differentranges of distances between the stent detector (300) and the stent.

The output device (320) may comprise one or more of a display device,audio device, and haptic device. In some variations, the display devicemay be configured to display a graphical user interface (GUI). A displaydevice may permit an operator to view patient data, sensor data, systemdata, alarms, and/or warnings. In some variations, an output device maycomprise a display device including at least one of a light emittingdiode (LED), liquid crystal display (LCD), electroluminescent display(ELD), plasma display panel (PDP), thin film transistor (TFT), organiclight emitting diodes (OLED), and the like. An audio device may audiblyoutput patient data, sensor data, system data, alarms, and/or warnings.For example, the audio device may output an audible warning when anoperator actuates the stent detector (300) to inject the needle (340)when a stent is not detected within a predetermined range by the stentdetector (300). In some variations, an audio device may comprise atleast one of a speaker, piezoelectric audio device, magnetostrictivespeaker, and/or digital speaker. A haptic device may provide additionalsensory output (e.g., force feedback) to the operator. For example, ahaptic device may generate a tactile response (e.g., vibration) toprovide an alarm and/or warning. For example, haptic feedback may notifythat operation of the cannulator is inhibited to prevent potential harmto the patient when a stent is not detected within a predeterminedrange. In some variations, the stent detector (300) may comprise a wiredand/or wireless transmitter configured to transmit a stent signal toanother device such as an external computing device including a desktopcomputer, server, database, and the like.

In some variations, a needle (340) may be advanced through the skin whenthe stent detector (300) locates the stent. The cannulator (330) maycomprise a lumen to guide the needle (340). The needle (340) may be maybe manually advanced from the cannulator (330) and/or actuated by thecannulator (330). The lumen may be configured to hold a needle (340) ofany suitable size for cannulation, such as between about 12 gauge andabout 20 gauge. The cannulator (330) may be configured to actuate whenthe stent is detected within a predetermined range to ensure that aneedle (340) will advance through an aperture of the stent. Operation ofthe cannulator (330) may be inhibited and a notification output when theoperator attempts to actuate the cannulator (330) when the stent isdetected outside a predetermined range.

The stent detector (300) may comprise one or more processors and one ormore machine-readable memories in communication with the one or moreprocessors. The processor may incorporate data received from memory,sensor data, and operator input to control the stent detector (300). Forexample, the processor and memory may receive the stent signal from thesensor and determine a distance of the sensor to a stent. In someinstance, the processor may compare the stent signal to a look-up-table.The processor may then select one or more notification methods based onthe determined distance and user settings. The memory may further storeinstructions to cause the processor to execute modules, processes and/orfunctions associated with the stent detector (300). The processor andmemory may be implemented consistent with numerous general purpose orspecial purpose computing systems or configurations. Various exemplarycomputing systems, environments, and/or configurations that may besuitable for use with the systems and devices disclosed herein mayinclude, but are not limited to software or other components within orembodied on computing devices such as routing/connectivity components,multiprocessor systems, microprocessor-based systems, distributedcomputing networks, personal computing devices, network appliances,portable (e.g., hand-held) or laptop devices.

The processor may be any suitable processing device configured to runand/or execute a set of instructions or code and may include one or moredata processors, image processors, graphics processing units, physicsprocessing units, digital signal processors, and/or central processingunits. The processor may be, for example, a general purpose processor,Field Programmable Gate Array (FPGA), an Application Specific IntegratedCircuit (ASIC), and/or the like. The processor may be configured to runand/or execute application processes and/or other modules, processesand/or functions associated with the system and/or a network associatedtherewith. The underlying device technologies may be provided in avariety of component types such as metal-oxide semiconductorfield-effect transistor (MOSFET) technologies like complementarymetal-oxide semiconductor (CMOS), bipolar technologies likeemitter-coupled logic (ECL), polymer technologies (e.g.,silicon-conjugated polymer and metal-conjugated polymer-metalstructures), mixed analog and digital, and/or the like.

In some variations, the memory may include a database and may be, forexample, a random access memory (RAM), a memory buffer, a hard drive, anerasable programmable read-only memory (EPROM), an electrically erasableread-only memory (EEPROM), a read-only memory (ROM), Flash memory, andthe like. As used herein, database refers to a data storage resource.The memory may store instructions to cause the processor to executemodules, processes and/or functions associated with the control system,such as stent detection, notification, calibration, cannulation, and/ordevice settings. In some variations, storage may be network-based andaccessible for one or more authorized users. Network-based storage maybe referred to as remote data storage or cloud data storage. Somevariations described herein relate to a computer storage product with anon-transitory computer-readable medium (also may be referred to as anon-transitory processor-readable medium) having instructions orcomputer code thereon for performing various computer-implementedoperations. The computer-readable medium (or processor-readable medium)is non-transitory in the sense that it does not include transitorypropagating signals per se (e.g., a propagating electromagnetic wavecarrying information on a transmission medium such as space or a cable).The media and computer code (also may be referred to as code oralgorithm) may be those designed and constructed for the specificpurpose or purposes. Examples of non-transitory computer-readable mediainclude, but are not limited to, magnetic storage media such as harddisks, floppy disks, and magnetic tape; optical storage media such asCompact Disc/Digital Video Discs (CD/DVDs); Compact Disc-Read OnlyMemories (CD-ROMs); holographic devices; magneto-optical storage mediasuch as optical disks; solid state storage devices such as a solid statedrive (SSD) and a solid state hybrid drive (SSHD); carrier wave signalprocessing modules; and hardware devices that are specially configuredto store and execute program code, such as Application-SpecificIntegrated Circuits (ASICs), Programmable Logic Devices (PLDs),Read-Only Memory (ROM), and Random-Access Memory (RAM) devices. Othervariations described herein relate to a computer program product, whichmay include, for example, the instructions and/or computer codedisclosed herein.

The systems, devices, and/or methods described herein may be performedby software (executed on hardware), hardware, or a combination thereof.Hardware modules may include, for example, a general-purpose processor(or microprocessor or microcontroller), a field programmable gate array(FPGA), and/or an application specific integrated circuit (ASIC).Software modules (executed on hardware) may be expressed in a variety ofsoftware languages (e.g., computer code), including C, C++, Java®,Python, Ruby, Visual Basic®, and/or other object-oriented, procedural,or other programming language and development tools. Examples ofcomputer code include, but are not limited to, micro-code ormicro-instructions, machine instructions, such as produced by acompiler, code used to produce a web service, and files containinghigher-level instructions that are executed by a computer using aninterpreter. Additional examples of computer code include, but are notlimited to, control signals, encrypted code, and compressed code.

C. Stent Delivery System

Generally, one or more stents may be advanced in a minimally invasivemanner through the vasculature and placed in the vein using a stentdelivery system. Generally, to deliver and deploy one or more stents,one or more catheters may be advanced in a minimally invasive fashionthrough the vasculature to a target location. In some instances, asingle catheter may be advanced to a target site in a blood vessel todeploy one or more stents. In other instances, a system comprisingmultiple catheters may be used to deliver and deploy one or more stentsto different target sites in respective blood vessels. For example, insome instances a catheter may be placed in each of the two blood vessels(e.g., different veins). The catheter may comprise a push wireconfigured to advance within the catheter to push one or more stents outof a lumen of the catheter for deployment of a stent. For example, oneor more stents may be pre-loaded into a lumen of the catheter distal tothe push wire prior to introduction through vasculature. The push wiremay be, for example, a guidewire, a stylet, a push rod, and the like.The push wire may be advanced within the catheter such that a distal endof the push wire pushes one or more stents out of the catheter and intoa target blood vessel. The stent may be configured to self-deploy to apredetermined shape when advanced out of the catheter and into a targetblood vessel by the push wire. In these instances, it should beappreciated that each catheter may or may not have the sameconfiguration of elements, and that some catheters may be different fromand/or complementary to other catheters. These devices and systems offera minimally invasive approach that may improve procedural speed bypermitting deployment of a plurality of struts using a single catheterand provide greater flexibility to allow stent delivery and deploymentusing smaller diameter blood vessels.

FIG. 6 illustrates a side view of a stent delivery system (600). Asshown in FIG. 6, a stent delivery system (600) may comprise a catheter(610), a proximal adaptor (620) coupled to a proximal end of thecatheter (610), a stent (630) configured to be compressed and advancedthrough the catheter (610), and a push wire (640) configured to push thestent (630) through and out of the catheter (610). The proximal adaptor(620) may help the stent transition from an expanded configuration to acompressed configuration to permit the stent to be advanced within alumen of the catheter (610). Although shown in FIG. 6 as having a singleport, the adaptor (620) may comprise any suitable number of ports (e.g.,zero, one, two, three, or four or more), and the port may serve one ormore useful functions (e.g., the introduction of one or more elements orsubstances into or through the catheter (610)). For example, theproximal adaptor (620) may be used to introduce one or more stents (630)into a lumen of the catheter (610). As another example, the proximaladaptor (620) may be used to introduce a fluid or substance (e.g.,contrast agents, flush agents, therapeutic agents, and/or intravenousfluids) into a body lumen (not shown), and may be connected to a liquidor gaseous fluid source (e.g., a fluid pump, a syringe, etc.). Theproximal adaptor (620) may further guide one or more devices (e.g., apush wire (640)) into a lumen of the catheter (610). Additional portsmay be provided as desired for other functions, such as a visualizationport, an actuator port, a suction port, and the like. Ports may have anysuitable connection form factor, such as a threaded connector, luerconnector, or the like.

In some variations, the one or more stents that may be loaded within alumen of the catheter may have the stent dimensions described herein. Insome instances, the stents may be configured to be compressible andbiased to transition from a compressed configuration to an expandedconfiguration (e.g., self-expand). In some variations, the diaphanousnature of the stent allows radial compression to a diameter of about0.035 inches or less, thereby allowing loading of the stent into a 4 Frcatheter or smaller. For example, the stent may be configured in acompressed configuration when loaded into a catheter and biased toself-expand to an expanded configuration when deployed from the catheterand into a target blood vessel having a larger diameter lumen than thecatheter. The catheters may have any suitable diameter for intravascularuse, such as, for example, about 4 French or less. Any suitable catheteror catheters may be used with the systems described herein to deploy thestents using the methods described herein. A push wire of the cathetermay have a diameter of up to an inner diameter of the catheter. The pushwire may have any suitable configuration (e.g., diameter) for pushingone or more loaded stents out of a distal end of the catheter. Thestents may have the same or different dimensions and characteristics.

D. Fistula Formation System

Also described here are systems for forming a fistula and improvingretrograde blood flow through peripheral vasculature. Generally, thesystems described here may comprise one or more catheters configured tobe used to form a fistula in addition to a stent. FIG. 4 shows anillustrative variation of a catheter system that may be used to form afistula as described herein. As shown there, the system may comprise afirst catheter (401) and a second catheter (403). The first catheter(401) may comprise a catheter body (405), one or more magnetic elements(407), and a fistula-forming element (409) that may be used to form afistula. In some variations, the fistula-forming element (409) may beadvanced to project out of an opening (411) in the catheter body (405).The fistula-forming element (409) may comprise an electrode configuredto move between a low-profile configuration and an extendedconfiguration in which it extends from the catheter body (405). In somevariations the fistula-forming element may be spring-biased toward theextended configuration. That is, the electrode may be configured toself-expand from the low-profile configuration to the extendedconfiguration. Put yet another way, the electrode (409) may be in itsnatural resting state in the extended configuration. In some variationsof electrodes moving between a low-profile configuration and an extendedconfiguration, the electrode may be held in the low-profileconfiguration during placement of the catheter. For example, in somevariations the electrode may be held in the low-profile configuration bythe catheter body. The electrode may be released from the low-profileconfiguration when the electrode has been delivered to the location forfistula formation. For example, in some variations, the electrode may bereleased by moving the electrode in a proximal direction relative to thehousing using a proximal control, as described in in U.S. patentapplication Ser. No. 13/298,169, filed on Nov. 16, 2011, and titled“DEVICES AND METHODS FOR FORMING A FISTULA,” which is herebyincorporated by reference in its entirety. In other variations, theelectrode may be held in a low-profile configuration by an externalradially inward force on the electrode from a vessel wall duringdelivery, as described in U.S. patent application Ser. No. 15/406,755,filed on Jan. 15, 2017, and titled “DEVICES AND METHODS FOR FORMING AFISTULA” and claiming the benefit of U.S. Provisional Application Ser.No. 62/399,471, filed on Sep. 25, 2016, and U.S. Provisional ApplicationSer. No. 62/279,603, filed on Jan. 15, 2016, the contents of each ofwhich are hereby incorporated by reference in its entirety.

In some variations, the first catheter (401) may comprise a housing(413), which may help protect other components of the first catheter(401) during fistula formation. For example, when the fistula-formingelement (409) comprises an electrode configured to ablate tissue, thehousing (413) may comprise one or more insulating materials which mayshield or otherwise protect one or more components of the first catheter(401) from heat that may be generated by the electrode during use.

As shown in FIG. 4, the second catheter (403) may also comprise acatheter body (415) and one or more magnetic elements (407). Invariations where the first catheter (401) comprises a fistula-formingelement (409) configured to project out the catheter body (405) of thefirst catheter (401), such as the variation depicted in FIG. 4, thecatheter body (415) of the second catheter (403) may comprise a recess(417) therein, which may be configured to receive the fistula-formingelement (409) as it passes through tissue. While shown in FIG. 4 ashaving a recess (417), it should also be appreciated that in somevariations the second catheter (403) may not comprise a recess (417). Insome variations, the second catheter may comprise a fistula-formingelement (not shown) in addition to or instead of the fistula-formingelement (409) of the first catheter (401). Thus, in some variations, afistula may be formed by one or more electrodes of one catheter, whilein other variations, two catheters each comprising an electrode maysimultaneously cut tissue from opposing sides to form a fistula.

Certain exemplary devices and systems that may be used in the methodsdescribed herein are described in more detail in U.S. patent applicationSer. No. 13/298,169, filed on Nov. 16, 2011, and titled “DEVICES ANDMETHODS FOR FORMING A FISTULA,” and U.S. patent application Ser. No.15/406,755, filed on Jan. 15, 2017, and titled “DEVICES AND METHODS FORFORMING A FISTULA,” the contents of each of which was previously herebyincorporated by reference in its entirety.

II. Methods

Described here are methods for aiding cannulation, improving retrogradeblood flow, and delivering a stent to a vessel using the systems anddevices described herein. Generally, the stents described herein may beused to aid in cannulation by assisting in locating the blood vesseland/or by structurally supporting the blood vessel during cannulation.For example, the stents may reduce damage and/or prevent collapse of ablood vessel being punctured during cannulation. Additionally oralternatively, the stents described herein may be used to increaseretrograde blood flow through a vein by being deployed into a veinsegment to hold open one or more venous valves to permit retrogradeblood flow. In some of these variations, a stent may be deployed inconjunction with formation of an arteriovenous fistula to providearterialized blood flow in a vein and/or aid cannulation of the fistula.

Generally, the stents described herein may be deployed by self-expansionor balloon expansion. For instance, a self-expanding stent in acompressed configuration may be constrained by a stent delivery system(e.g., a system comprising a conduit configured to hold theself-expanding stent in a compressed configuration) as it is advancedthrough vasculature in a minimally-invasive manner. Upon delivery to atarget vessel by the stent delivery system, the self-expanding stent maytransition from the compressed configuration to an expandedconfiguration. The stent delivery system may be withdrawn from thetarget vessel and the stent may remain within the target vessel.Similarly, a balloon expandable stent in a compressed configuration maybe coupled to a stent delivery system comprising a deflated balloon asit is advanced through vasculature in a minimally-invasive manner. At adeployment location, the balloon of the stent delivery system may beinflated to expandably deform the stent to an expanded configuration.After the balloon is deflated, and the stent delivery system withdrawn,the stent may remain in the expanded configuration within the targetvessel.

In some variations, blood flow in a vessel may be improved using thecatheters, stents, and corresponding methods described in U.S. patentapplication Ser. No. 15/406,755, filed on Jan. 15, 2017, and titled“DEVICES AND METHODS FOR FORMING A FISTULA” and claiming the benefit ofU.S. Provisional Application Ser. No. 62/399,471, filed on Sep. 25,2016, and U.S. Provisional Application Ser. No. 62/279,603, filed onJan. 15, 2016, the contents of each of which was previously herebyincorporated by reference in its entirety.

A. Cannulation

In some variations of the methods described here, the stents describedherein may be used to aid in cannulation, such as by assisting inlocating the blood vessel, and/or by structurally supporting the bloodvessel during cannulation. FIG. 5A illustrates a cross-sectional view ofa vessel and stent for cannulation. A stent (500) may be disposed in ablood vessel (502) beneath the skin (506). When the stent (500) islocated in a vessel (502) having valves (504) (e.g., a peripheral vein),the stent (500) may be configured to hold open the valves (504). FIG. 5Adepicts a needle (516) being inserted into the skin (506), blood vessel(502), and stent (500). In some variations, a stent (500) disposed in avessel (502) may be more palpable than the vessel (502) alone, and thusmay assist in location of the vessel (502). For example, when the skin(506) is palpated, the stent (500) may exhibit tympanic characteristicsthat may help an operator define a vessel and determine an access site.

A stent may additionally or alternatively assist in location of thevessel by allowing other forms of detection. For example, a stentdetector may be used to locate the stent and therefore locate the bloodvessel in which the stent is disposed. In some variations, a sensor of astent detector may comprise a metal detector configured to detect ametal content of a stent disposed in a blood vessel. For example, thestent detector may be swept over a patient's skin. This may be usefulwhere visualization and palpation of a vein is difficult due to a thicklayer of adipose tissue. An example is shown in FIG. 5B where a stentdetector (510) may be used to locate the stent (500), and therefore, theblood vessel (502) to be cannulated. The stent detector (510) may, forexample, generate a magnetic field (511) used to detect a property ofthe stent (500) (e.g., metal). A display device (512) using one or moreLEDs in FIG. 5B may indicate that a weak return signal of the stent(500) has been detected such that the stent detector (510) is near butnot directly above the blood vessel (502). For example, a single LEDemitting red light may indicate that the stent is within a peripheralsensor range of the stent detector. The color, intensity, pattern, etc.of the LED may change as the stent signal changes.

As shown in FIG. 5C, as an operator moves the stent detector (510) overthe skin, the display (512) of the stent detector (510) may indicatethat the stent detector (510) and cannulator (514) are located above theblood vessel (502) and stent (500) in a desired position forcannulation. For example, two LEDS may emit a green light that mayindicate that the stent is below the stent detector within apredetermined sensor range. In this manner, the blood vessel (502) forcannulation may be located even through thick layers of adipose tissue.In some variations, a needle (516) may be loaded in a lumen of thecannulator (514) for advancement through the skin (506), blood vessel(502), and stent (500). These devices and systems offer a non-invasiveapproach to determining a blood vessel location, having improvedprocedural speed.

A stent may additionally or alternatively assist in cannulation bystructurally supporting the blood vessel during cannulation. Forexample, in some cases, cannulation of an arterialized vein may collapsethe vein due to insufficient blood pressure. However, a stent disposedin a vein segment may increase the strength and stiffness of a portionof the vein to withstand cannulation without vein collapse and/orback-walling of the needle. Furthermore, cannulation of a vein may insome cases cause infiltration of the vein where blood leaks out of thevein and causes swelling in the perivascular space (e.g., hematoma).Infiltration may compress the vessel and cause an undesirablethrombosis. A stent disposed in the blood vessel may increase the radialstrength of the vessel to reduce the compressive forces of cannulationand infiltration from closing the blood vessel shut.

B. Retrograde Flow

The methods described herein may also increase retrograde blood flowthrough a vein. Generally, the methods may comprise advancing one ormore stents into peripheral vasculature. The stent may be deployed intoa vein segment to hold open one or more valves. The stent may provideforce on the venous valves to hold the leaflets of the valves in an openconfiguration. As such, the stent may hold one or more venous valves tofrustrate the valves without cutting them. Furthermore, deployment ofthe stent may be faster and simpler than use of a valvulotome. Forinstance, deployment of the stent in a vessel may be performed withoutvisualization (e.g., contrast injection) due to the symmetric andrepeating configuration of the stent. Moreover, the sidewalls of thestent may additively increase the radial strength of the vein vesselwalls, as described in more detail herein.

As mentioned above, use of a stent in venous tissue to frustrate one ormore venous valves may be performed in fewer steps than a valvulotomy. Avalvulotomy procedure to increase retrograde blood flow through a veinmay require a user to visualize and locate a valve (e.g., usingcontrast), unsheathe the valvulotome, cut the leaflets with thevalvulotome, resheath the valvulotome, and repeat the process for eachvalve to be cut. This may be a time consuming process, as the location,size, and spacing of valves in peripheral vasculature varies perindividual. By contrast, a venous stent having a length sufficient tocover a desired vein segment may be located and deployed once to hold aplurality of valves in an open configuration irrespective of thelocation, size, and spacing of the valves. Put another way, a venousstent may in some instances prevent valve function over a desired veinsegment in fewer steps and less time than a valvulotome. In addition,use of a venous stent to frustrate valves may be reversible (i.e., thestent may be removed from the vein to regain valve function), incontrast to a valvulotomy.

A length of a stent may be varied based on a desired length ofretrograde blood flow in the vessel. For example, a longer stentdisposed in a vein segment will cover and render incompetent a greaternumber of venous valves and thus allow for distal blood flow along agreater length of the vein. It may be desirable for the distal portionof the stent to have a minimal thickness and surface area necessary tohold open the venous valves.

In some variations, a stent may also increase retrograde blood flowthrough a vein by forming a proximal thrombus. For example, a stent maybe configured to form a thrombus after being delivered to a vessel.Blood flow through the fistula may be thus be diverted distally to flowretrograde through the vein at a predetermined rate (e.g., over a week).A proximal portion of a stent may comprise, for example, copper toinduce a thrombus over time. In other variations, the proximal portionof the stent may be electroplated, comprise a coating for inducingthrombosis, and/or be made of a thrombogenic fiber. Alternatively, theproximal portion of the stent may comprise a semi-permeable orimpermeable membrane (e.g., cap, plug) to immediately reduce and/oreliminate proximal venous blood flow back to the heart. A distal portionof the stent may be configured to permit unobstructed blood flow througha lumen of the vein (e.g., by frustrating the venous valves). The distalportion may in some variations be configured to prevent plateletaggregation and maximize retrograde blood flow through the vein.

C. In Conjunction with a Fistula

The systems and methods described here may be used in some variationsfor cannulation of a fistula, such as for dialysis access. In somevariations, the methods may comprise deploying a stent in conjunctionwith formation of an arteriovenous fistula to ease cannulation of thefistula, and/or to allow for additional cannulation sites. The fistulamay in some variations be a surgically formed fistula. In othervariations, the fistula may be formed by a minimally invasive procedure.For example, the fistula may be formed endovascularly using a cathetersystem as described herein.

More particularly, in some variations a fistula may be formed using aminimally invasive procedure by accessing a first blood vessel with afirst catheter, and advancing the first catheter to a target locationwithin a first blood vessel. A second blood vessel may be accessed witha second catheter, and the second catheter may be advanced to a targetlocation within the second vessel. After the vessels are brought towardeach other and aligned, one or more fistula-forming elements may beactivated to bore through, perforate, or otherwise create a passagewaybetween the two blood vessels such that blood may flow directly betweenthe two adjoining blood vessels.

In some variations of methods in which a fistula is formed using acatheter system, the methods described herein may comprise aligning thefirst and second catheters. This may axially and/or rotationally alignthe catheters. For example, the catheters may be oriented such that afistula-forming element of at least one of the first or second catheteris positioned to form a fistula in a certain location. In variationswhere both the first and second catheters comprise fistula-formingelements (e.g., an active electrode and a ground electrode, or each anactive electrode), the catheters may be oriented to align thesefistula-forming elements. The catheters may be aligned in any suitablemanner. The first and second catheters may comprise any alignmentelement or combination of alignment elements. In some variations, eachof the first and second catheters may comprise one or more magneticalignment elements, which may generate an attractive force between thefirst and second catheters. This may pull the catheters toward eachother and/or help to rotationally align them. Once the catheter orcatheters are in position, one or more fistula-forming elements may beused to create a fistula between the two blood vessels, as described inmore detail in U.S. patent application Ser. No. 13/298,169, filed onNov. 16, 2011, and titled “DEVICES AND METHODS FOR FORMING A FISTULA,”and U.S. patent application Ser. No. 15/406,755, filed on Jan. 15, 2017,and titled “DEVICES AND METHODS FOR FORMING A FISTULA,” each of whichwas previously incorporated by reference in its entirety.

The methods involving stents described herein may allow for easiercannulation of a fistula, for example to allow for dialysis access, byassisting with locating the access site and/or by structurallysupporting the blood vessel during cannulation, as described in moredetail herein. Furthermore, the methods involving stents describedherein may allow for additional cannulation sites by allowing forretrograde flow. For example, a venous stent may allow for cannulationin the forearm region of a patient. This may be desirable because avessel for vascular access in hemodialysis is ideally located about 5 mmor less from the skin of the patient. However, some vessels,particularly in the upper arm, may be too deep below the skin forpalpation and/or visualization due to an underlying layer of adiposetissue.

In some variations, the methods described herein may comprise forming afistula and deploying a stent in vein, such as a cephalic vein and/orbasilic vein. Arterialized blood flow may flow distally from the fistulaand through the stent until meeting one or more accessory branches, atwhich point a portion of the retrograde blood may flow proximallythrough the one more accessory branches proximally towards the heart.Thus, the stent may define or expand a cannulation region (e.g., veinsegment) having arterialized retrograde blood flow. In one particularvariation, a stent as described herein may be deployed in the cephalicvein to frustrate the venous valves and allow for retrograde flow from afistula distally. The stent may be placed distal to or through theregion of the elbow crease and the forearm until the cephalic vein meetsthe accessory cephalic vein. This may allow cannulation of the cephalicvein in the forearm region. In this example, blood flow may returnproximally via the accessory cephalic vein. The stent may additionallyassist with cannulation in the forearm region by assisting with locatingthe vessel and structurally supporting the vein, as described herein.

Additionally or alternatively, a portion of a stent located in a veinproximally to a fistula may be used to form a thrombosis to drivearterial blood flow distally through the vein. In some of thesevariations, a portion of the stent may cover the fistula, and blood flowthrough the fistula may travel through the sidewall of the stent. Thestent may form a thrombus as described in more detail herein. Forexample, a proximal portion of the stent may comprise copper to inducethrombus over time (e.g., a week). In other variations, the proximalportion of the stent may be electroplated, comprise a coating forinducing thrombosis, and/or be made of a thrombogenic fiber.Alternatively, the proximal portion of the stent may comprise asemi-permeable or impermeable membrane (e.g., cap, plug) to immediatelyreduce and/or eliminate proximal venous blood flow back to the heart. Anintermediate portion of the stent, disposed between a proximal portionand a distal portion, may be disposed over a fistula and may be porousto permit blood flow from the fistula to flow into the vein. A distalportion of the stent may be configured to permit unobstructed blood flowthrough a lumen of the vein (e.g., by frustrating the venous valves).

D. Stent Delivery

The methods described herein may also deliver one or more of the stentsdescribed herein into a target vessel. Generally, the methods maycomprise advancing and deploying one or more stents into peripheralvasculature using a single catheter. The use of the devices and systemsdescribed herein may be performed in fewer steps than using conventionalstent delivery systems. Typical stent delivery systems include acatheter provided individually per stent. For example, a single stent istypically affixed to an end of a catheter and covered by an outer sleeveduring advancement through vasculature. Once the stent is advanced to adesired location, the outer sleeve may be retracted so as to allow thestent to expand (e.g., using self-expansion and/or balloon expansion)and deploy into a target blood vessel. These systems using a catheterand sleeve are typically 6 French and greater in diameter. Accordingly,deployment of a plurality of stents may be a time consuming process thatrequires a set of corresponding delivery systems. By contrast, the stentdelivery methods and systems described herein provide an easily operatedand adaptable catheter that may be configured to deploy a plurality ofstents sequentially without advancing and withdrawing individualcatheters. Put another way, one or more stents may in some instances bedeployed into one or more target blood vessel segments in fewer stepsand less time than conventional stent delivery systems. The stents mayhave different configurations and be loaded sequentially together in thecatheter. The stents may be configured with different dimensions,characteristics, and functions. For example, stents configured forvessel support may differ in one or more of materials, compressibility,detection, diameter, strut thickness, etc., from stents configured forvessel visualization. In addition, the stent delivery cathetersdescribed herein may have a compact configuration that allowsadvancement and deployment of stents in small diameter vessels.

In some variations, one or more stents may be deployed using a minimallyinvasive procedure by accessing a blood vessel with a catheter, andadvancing the catheter to a target location within the blood vessel.FIGS. 7A-7E show illustrative steps of a method for delivering a stent(730). FIG. 7A illustrates a cross-sectional side view of a proximal endof a stent delivery system (700) with a stent (730) in position to beinserted into a lumen of the catheter (710). The stent (730) may beintroduced into a proximal end of a catheter (710) through a proximaladaptor (720). The system (700) may include a catheter (710) coupled tothe proximal adaptor (720). In some variations, the stent (730) may bebiased to be in an expanded configuration (as shown in FIG. 7A). FIGS.7B and 7C are respective cross-sectional side and perspective views ofthe stent (730) and a push wire (740) being introduced into a proximalopening of the proximal adaptor (720). An inner diameter of the adaptor(720) may taper to match the catheter (710) coupled to the adaptor(720). As the stent (730) in an expanded configuration is introducedfurther into the adaptor (720), the inner diameter of the adaptor (720)decreases and the diaphanous stent (730) may begin to transition fromthe expanded configuration into a compressed configuration, therebyallowing the stent (730) to be introduced into a proximal end of thecatheter (710) and slidably advanced in the compressed configuration. Asthe push wire (740) is introduced into the catheter (710), the adaptor(720) may guide the push wire (740) into a lumen of the catheter (710).For ease of illustration in FIGS. 7B and 7C, stent (730) and push wire(740) are shown as being introduced together into the adaptor (720).However, one or more stents (730) may be introduced sequentially intothe catheter (710) prior to the push wire (740) such that a proximal endof one of the stents (730) may abut a distal end of the push wire (740).

FIG. 7D illustrates a cross-sectional side view of a stent (730) in acompressed configuration within a lumen of the catheter (710). Thestents may have the same or different configuration, so long as they maybe disposed within a lumen of the catheter (710) in a compressedconfiguration. In some variations, the catheter (710) may be loaded withone or more stents (730) outside of the body. The push wire (740) may beadvanced into the catheter (710) and disposed proximal to the loadedstents (730). In other variations, the catheter (710) may be introducedand advanced into vasculature in a minimally invasive manner prior toloading the catheter (710) with one or more stents (730) and push wire(740). Additionally or alternatively, a first set of stents may beintroduced into the catheter (710) prior to a minimally invasiveprocedure. After the deployment of the first set of stents in one ormore target vessels, the catheter (710) may be repositioned at a desiredlocation, the push wire (740) may be retracted from a proximal end ofthe catheter (710), and a second set of stents may be introduced andloaded into the catheter (710).

Once a distal end of the catheter (710) is positioned at a predetermineddeployment location, the push wire (740) may be advanced within thecatheter (710) to push the one or more stents (730) out of the distalend of the catheter (710) and into the target blood vessel. FIG. 7E is aperspective view of the catheter system (700) deploying a stent from adistal end of the catheter (710). Although not shown in FIG. 7E, adistal end (e.g., distal tip) of the push wire (740) may contact andpush a proximal end of the stent (730) while the catheter (710) isstationary relative to the target blood vessel so as to advance thestent (730) out of the catheter (710) and deploy the stent (730) in thetarget blood vessel. Alternatively, the stent (730) may be advanced anddeployed out of the catheter (710) by retracting the catheter (710)while the push wire (740) is stationary relative to the target bloodvessel.

In some variations, the stent (730) disposed in the catheter (710) is ina compressed configuration and transitions to an expanded configurationupon advancement out of the catheter (710) and into the target bloodvessel. For example, the stent (730) may self-expand as the stent (730)is advanced into the target blood vessel having a larger diameter lumenthan that of the catheter (710). In other variations, a balloon may beused to transition the stent into an expanded configuration throughballoon inflation.

In variations in which a plurality of stents (730) are to be deployed,the stents (730) may be deployed in a sequential manner by advancementof the push wire (740) and/or retraction of the catheter (710). As onenon-limiting example, a first stent may be deployed in a first bloodvessel (e.g., vein) portion by advancing the push wire (740) to push thefirst stent out of the catheter (710) while the catheter (710) remainsfixed relative to the first blood vessel. The first stent mayself-expand (e.g., bias to form the expanded configuration) oncedisposed in the first blood vessel. The catheter (710) may be advancedthrough vasculature to another predetermined location and then used todeploy a second stent in a second vein portion by further advancing thepush wire (740) to push the second stent out of the catheter (710). Athird stent may be deployed in the second vein portion by retracting thecatheter (710) relative to the second vein portion while maintaining thepush wire (740) in position. The second and third stents may self-expandonce disposed in the target blood vessel.

Although the foregoing variations have, for the purposes of clarity andunderstanding, been described in some detail by of illustration andexample, it will be apparent that certain changes and modifications maybe practiced, and are intended to fall within the scope of the appendedclaims. Additionally, it should be understood that the components andcharacteristics of the devices described herein may be used in anycombination. The description of certain elements or characteristics withrespect to a specific figure are not intended to be limiting or norshould they be interpreted to suggest that the element cannot be used incombination with any of the other described elements.

We claim:
 1. A method for cannulating a first vessel comprising:advancing a stent into the first vessel comprising one or more valves;deploying the stent over the one or more valves to hold open the one ormore valves; non-invasively detecting a stent location of the stent witha stent detector; and advancing a needle through a wall of the firstvessel, wherein the stent detector is coupled to a needle injector ofthe needle.
 2. The method of claim 1, wherein the needle is advancedthrough an aperture defined in a wall of the stent.
 3. The method ofclaim 1, wherein the needle is advanced through the wall of the firstvessel distal to the stent.
 4. The method of claim 1, further comprisingpositioning the needle over the first vessel using the detected stentlocation.
 5. The method of claim 1, wherein the stent comprises firststruts and second struts having different thicknesses.
 6. The method ofclaim 1, wherein the first vessel is a cephalic vein.
 7. The method ofclaim 1, wherein the first vessel is a basilic vein.
 8. The method ofclaim 1, further comprising advancing a first catheter into an arteryadjacent to a vein, wherein the first catheter comprises afistula-forming element, and forming a fistula between the artery andthe vein using the fistula-forming element.
 9. The method of claim 8,wherein the stent is deployed distal to the fistula.
 10. The method ofclaim 8, wherein the artery is an ulnar artery and the vein is an ulnarvein.
 11. The method of claim 8, further comprising advancing a secondcatheter into the vein.
 12. The method of claim 11, further comprisingaligning the first catheter and the second catheter.
 13. The method ofclaim 1, further comprising loading one or more stents into a thirdcatheter, and deploying the one or more stents sequentially from thethird catheter into the first vessel by advancing a push wire throughthe third catheter.